The present invention relates to a tool path creation apparatus such as a CAM (Computer Aided Manufacturing) system, and more particularly to a tool path creation apparatus suitable for rough cutting for cutting a work into a shape to be used for finish cutting.
In conventional rough cutting, less than 3 axis milling has been mainly used as described in “Die Technology” (Vol. 13, No. 9, THE NIKKAN KOUGYO SHIMBUN LTD), pp. 27–31 (hereinafter called Reference 1). Reference 1 describes some methods for rough cutting. In one method, surface data on the work shape and the finishing shape is input to create straight lines from the work surface to the finished surface and then drills are used for boring. In another method, the cross sections from the work surface to the finished surface are created and a tool path that is the offset of the inner or outer cross section curve is used. In still another method, those two methods are combined. Reference 1 also discloses that a rapid change in the cutting path direction, sometimes caused during rough cutting depending upon the shape, may damage the tool. The method for creating intermediate cross section curves from the outer and inner cross section curves is described on pages 17–36 in “On the Computational Geometry of Pocket Machining” (M. Held, Springer-Verlag Berlin Heidelberg, 1991, Printed in Germany) (hereinafter called Reference 2). Reference 2 describes some methods for creating intermediate cross section curves. In one method, the outer and inner cross section curves are offset and the intermediate cross section curves are created with the auto-crossing curves in the cutting path direction removed. In another method, the power diagram (voronoi diagram) of the outer and inner cross section curves are used to create intermediate cross section curves. For the voronoi diagram, the basic concept and the processing on a computer are described on pages 131–185 in “Bit separate Volume Computer Science, acm Computing Surveys' 91”.
Another method for rough cutting is that the difference between the work shape and the finishing shape is used to represent an intermediate shape and, from this intermediate shape, the cutting data is created. For example, a method for creating the intermediate shape of a rotary object from the difference between the work solid shape and the finished solid shape to create a rotary shape for use in cutting is described on pages 316–318 in “A Manufacturing Process Drafting in SUPOG: Support System for Drawing Operation-Guide-Document” (collected papers (V) for the 72nd national convention of The Japan Society of Mechanical Engineers).
In addition, the creation of a solid body by interpolating a surface is described on pages 3224–3226 in “Research on an Algorith for Automatic Finite Element Mesh Generation Related to the Geometric Model” (No. 484, Volume C of collected papers of The Japan Society of Mechanical Engineers, December, 1986). The creation of a skinned surface is described on pages 457–471 in “The NURBS Book 2nd Edition” (Les Piegl, Wayne Tiller, Springer-Verlag Berlin Heidelberg, 1995 and 1997, printed in Germany) (hereinafter called Reference 3).
On the other hand, it is easy for a tool-path creating CAM using more than 4 axis milling (hereinafter called a multi axis CAM) to create a tool path for cutting into a work shape and to create a tool path for cutting into a finishing shape. A multi axis CAM can output a tool path into a file in a standard format of APT (Automatically Programmed Tools: developed in 1995 by Massachusetts Institute of Technology of United States).